Charged particle angular momentum changer



y 7, 1965 R. c. WINGERSON 3,197,630

CHARGED PARTICLE ANGULAR MOMENTUM CHANGER Filed March 13, 1962 2Sheets-Sheet 1 W INVENTOR. m rj J x 53 H65 gllCHARD C.WINGERSON AGENTJuly 27, 1965 CHARGED PARTICLE SOURCE R. C. WINGERSON CHARGED PARTICLEANGULAR MOMENTUM CHANGER Filed March 13, 1962 2 Sheets-Sheet 2 CHARGED15 |4 PARTICLE SOURCE 12 V v v 84 83 ii 85 FIG. 8 T

42 42 I 42 1 41 9 e @c 44 1 1 MW? W43 A INVENTOR. x gcHARD C.WINGERSONF/G. 7 flaw AGENT United States Patent (IHARGED PARTHCLE ANGULARMGMENTUM QHANGER Richard Q. Wingerson, Dayton, (this, assignor toMassachusetts Institute of Technology, Qamhridge, Mass, a

corporation of Massachusetts Filed Mar. 13, 1962, Ser. No. 179,419 1?Claims. (Cl. 3l7-2tltl) This invention relates to a method and apparatusfor changing the angular momentum of a charged particle. Moreparticularly, to means for changing the proportion of the energy of acharged particle between energy con ponents parallel to andperpendicular to an almost uniform magnetic field without necessarilychanging the total energy of the particle or the average strength of thefield.

It is an axiom or physics that a charged particle injected into anystatic magnetic field configuraton will not be trapped, unless itsenergy is changed While it is Within the field. As a result of thisprinciple, ions injected from an ion source into a static magnetic fielddo not remain in the magnetic field for a time as long as might bedesired. This situation exists with present methods for introducing ionsinto a thermonuclear device such as a magnetic mirror. There is greatditliculty in introducing ions into the active region of the magneticmirror in such a way that the ions are retained in the active region fora time period great enough to permit the ionic collisions to causesubstantial numbers of fusion reactions. Also, other devices such as thesynchrotron require that the electron or charged particle be introducedon a path as near as possible approximating the orbit of the chargedparticles already being energized by the synchrotron. This introductionof charged particles is a difiicult problem and is achieved presentlyonly at the expense or" complex and intricate apparatus.

it is, therefore, a primary object of this invention to provide a devicewhich will change the orbit of a charged particle by a unique magneticor electric field configuration.

it is possible to change the energy components of a charged particle bymeans of a magnetic field of nonuniform intensity. The energy componentsreferred to are those in the axial direction and the angular momentumcomponent around the axis. plishes this interchange of ener y componentsby developing a radial component of flux density at all regions withinthe mirror. Another technique for interchanging energy components bydeveloping a radial component of flux density is described in 1. Tech.Phys. U.S.S.R. 39, 249 (i960) [translationz Soviet Phys-Tech Phys. 5,229 (196%)] where axially spaced coils produce a variable density axialfield having a radial field component which varies in intensity anddirection along the axis of the coils. Both of these devices arebilateral devices in that they do not discriminate in their effect onparticles regardless of the axial direction of the particle velocity.Also, in the case of the magnetic mirror, at least, magnetic moment isconstant. Magnetic moment is defined as /2mV /B where m is the mass ofthe charged particle, V is the velocity component of the chargedparticle transverse to the magnetic field intensity B These devices areto be distinguished from the device of the present application which ishighly unidirectional in the sense that the device is etlective incausing substantial change of longitudinal and transverse velocities ofa charged particle when the particle is travelling in one directionwhereas it will produce only minor perturbation on the particle whentravelling in the opposite direction.

It is, therefore, another object of this invention to provide a devicewhich is unidirectional in its efiect upon the motion of a chargedparticle.

A magnetic mirror accom-- 3,l@7,fi8 Patented July 27, 1965 A particlehaving a trajectory in a static magnetic field and having energycomponents in a direction perpendicular to and parallel to the magneticfield has a property called adiabaticity wherein the magnetic moment ofthe particle tends to remain constant. This adiabaticity is oftenexploited in controlling particle motion. However, it is sometimesdesired that the magnetic moment be changed. At present, this isextremely difiicult to accomplish. It is possible to either increase ordecrease particle magnetic moment in a controlled way by means of thedevice of this invention.

It is still another property of this device that the magnetic moment or"the charged particle can be changed without changing its total energy.

These and other objects and advantages will become apparent from aconsideration or" the following specification and drawings, wherein:

FIGURE 1 is a diagram showing the forces exerted on a moving chargedparticle in a magnetic field.

FIGURE 2 shows a schematic diagram of a coil of variable pitch showingthe trajectory of a resonant charged particle as its magnetic momentchanges.

FIGURE 3 is a cross-sectional view of a variable pitch coil offerromagnetic material showing the transverse field perturbation.

FIGURE 4 shows the coil of FEGURE 3 used in conjunction with a magneticmirror.

FlGURE 5 is a cross-sectional view of a current-carrying coil ofvariable pitch showing the magnetic field pattern.

FIGURE 6 is an axially transverse cross-section of a quadrafile coilshowing the field pattern.

FIGURE 7 is an electrostatic bifilar coil.

FIGURE 8 shows the coil of FIGURE 2 used in conjunction with a sectionof a particle accelerator.

In order to understand the principles of operation of the invention, thefundamental force equation on a moving particle of mass m and charge qand how this equation is applied in the invention is considered. In FlG-URE la, a particle of positive charge q having a velocity V along the Zaxis is subjected to a transverse force F along the X axis by theinfluence or the transverse magnetic field E along the Y axis, F qV iiFIGURE lb shows the resulting component of velocity V of the particle inthe direction of force F Velocity V of the charged particle causes aforce F to be exerted upon the particle because of the effect oftransverse field B The force F is exerted along the axis Z in adirection to cause the particle to slow down from its original velocityV The transverse velocity V also causes a force F of FIGURE 10 to beexerted on the particle because of the influence of the longitudinalfield B This force F is radially directed so that it will cause theparticle to have a radial acceleration which causes the particle toassume a trajectory of circular cross section. Thus, it is seen thatbecause of the transverse field E the particle has had its longitudinalvelocity V decreased, has acquired a transverse velocity V and has beenconstrained by the longitudinal field B to follow a circular orbit. if Band B were of indefinite extent, the particle would follow a spiraltrajectory which would have its longitudinal axis in the direction ofthe vector sum of B and B and would have a circular path about this axisof constant'radius r and of constant pitch p along this axis.

If it is desired to change the pitch without changing the energy of theparticle, it is necessary to cause the particle energy in thelongitudinal direction /2mV to be transferred in part to energy in thetransverse direction, /2mV Since B reacting with V produces a force Fopposing the velocity V a device which will cause B to be continuouslytransverse to V is desired. since V will continuously change directionunder the influence of B a transverse magnetic field B which changesdirection in unison with the transverse velocity V will result in acondition where E and V are continuously at right angles-21 conditionwhich will produce maximum force F (and change in velocity V;,). Sincethe energy of the particle remains constant, a decrease in V must beaccompanied by an increase in V Thus the pitch (p 2qrmV /fi q) of thespiral trajectory of the particle decreases and the radius (r mV- /B q)of the cross section of the trajectory increases. Since E is rotating indirection as the particle proceeds in a direction along the Z axis, thelongitudinal axis of the particle trajectory is along the Z axis ratherthan off the axis a in the case where E is only in the Y axis direction.

It is seen that a charged particle can be made to transfer energy fromone component of velocity to another component of velocity transversethereto by a magnetic field which is transverse to both velocitycomponents and a second magnetic field in parallel with the component ofvelocity which is not changing direction. Whether the transfer is fromthe energy in the longitudinal velocity component V to energy in thetransverse velocity component V or conversely depends upon the directionof the longitudinal field B the charge on the particle.

This invention is concerned principally with devices for achievingenergy transfer between longitudinal and transverse velocity energycomponents by providing a transverse magnetic field which is twisted sothat the transverse field is always perpendicular to the transversecomponent of velocity of a charged particle. Devices can also bedesigned utilizing a twisted electric field rather than a twistedmagnetic field. The performance of these electric devices will be sosimilar to that of the magnetic types that they will be mentioned onlywhen explicit differences are to be noted.

The objects stated above have been obtained in the present invention byproviding a magnetic field which has a particular spatial variation. Aproperly designed helical field source (a corkscrew) can perturb aninitially uniform axial field in such a way that there will be amonotonic increase (or decrease) in the transverse energy component ofcertain particles traversing the structure. The necessary designcondition for the device is that the force resulting from theinteraction of the axial particle velocity with the transverse componentof the field perturbation be always approximately in the direction ofthe transverse particle velocity. It follows that there must be a closematch between the local pitch of the device and that of the modifiedhelical particle trajectory. This condition may be expressed as ptz)where B is the unperturbed axial field intensity, m, q and V(z) are themass, charge, and axial velocity of the particle, and 7(1) is thecorkscrew pitch length at position 2 (p is negative for the left-handedstructure of FIG- URE 2). The helical field perturbation has no over-alleffect on the axial field B therefore, a change in the transverseparticle energy necessitates a change in magnetic moment. The trajectoryill in FIGURE 2 could apply to an ion moving from left to right or to anelectron moving from right to left. If the direction of B i reversedfrom that shown in FIGURE 2 the trajectory 11 applies to an electronmoving 11'01'11 left to right 'or to an ion moving from right to left.If the variable pitch coil 1 is wound as a right hand spiral (instead ofleft hand as shown in FIGURE 2), the terms ion and electron must beinterchanged in the preceding two sentences; and the spiral trajectorybecomes right handed. Reversing the polarity of source 15 connection tocoil 14 reverses the direction of transverse flux E at any axialposition 2'. This reversal causes the trajectory ill to rotate 180 inangle 6 about the z axis; otherwise, the trajectory is unaffected.

FIGURE 2 shows one form of a corkscrew device where a source for chargedparticles having some velocity energy has not been shown (the source maybe located at either end of the corkscrew and may emit either elec tronsor positive or negative ions provided 5;, is given the correct polarityand the particles have the correct entrance conditions). A load whichuses the electron stream ll has not been shown in order to avoidobscuring the basic corckscrew device. A field coil 12 energized bysource 13 produces a longitudinal magnetic field B A coil 14 of variablepitch p is immersed in field 8;, with the coil axis 2 parallel to thefield B Coil i4 is energized by source 15 to produce a magnetic fieldhaving a component transverse to axis z. This transverse magnetic fieldvaries in intensity and direction as a function of axial position insidecoil lid but as a first approximation may be considered to be directednormal to the z axis and normal to the conductor forming coil lid. Thusthe transverse field has a spiral shape (or more correctly an augershape) closely following the spiral of coil il s.

A transverse magnetic field which is twisted may be obtained in severalways. Most configurations, including the most practical ones, are notsusceptible to analysis. As a result, an idealized case will beconsidered.

An infinitely long conducting ribbon wound into a helix with uniformpitch, radius r carrying a current I, and w/ p the fraction of cylindersurface covered by the ribbon, has fields on the axis given by B u f/ pand where z and 0 are the field coordinates with origin at a radius linepassing through the center of the conducting ribbon, the KS arel-l'ankel functions, and r is the cyclotron radius of the particle inthe axial field. If desired, the expression is readily integrated withrespect to r to allow for a coil of finite thickness as well as width.

Although the above equation is for an infinitely long helix of constantpitch, the equation is useful in approximating the field configurationsof a variable pitch helix since the field produced falls off rapidlywith distance and a new pitch value can be used at different parts ofthe variable pitch helix.

It is seen that a transverse field which rotates with particle positionis required. There are many ways in which this field can be produced.Among the simplest of these devices from a construction standpoint is anappropriate helix of magnetic material immersed in a magnetic field. Adesign which was successful in causing an electron beam to wind-up to anextent where approximately half of the energy was in the transverseenergy. component was constructed from a piece of mild steel bar stock,/8 inch thick by 30 inches long and tapered from a width of 0.5 inch atthe center to zero at the ends in a cosine manner. The bar was woundinto a helix of 1 inch inside diameter with a pitch length of 1 inch atthe center decreasing in pitch as the ends are approached in a uniformmanner so that the overall length is approximately four inches. Thetaper down to zero width at the ends of the coil provides a smalltransverse field so that the electron is not deflected from the axis bya large discontinuity in the field. The helix is constructedsymmetrically about its center; the first half merely serves as an inletstructure to avoid spurious beam perturbations, the actual electron beamwindup occurring in the exit half of the coil. The length of theeffective part of the structure was approximately twice that calculatedto be necessary to produce the wind up achieved. The excess lengthprovides a mechanism for phase stability of the beam trajectory. Thisoccurs because for any angular position of the electron, the value oftransverse field will depend on the axial position of the oneness ielectron. If the electron is advanced in axial position over its designposition, the transverse field is stronger and reduces the axialvelocity of the electron and similarly for an electron retarded in axialposition where the transverse field is weaker.

FIGURE 3 shows the iron coil Fill with a coil 32 and energy source 33.The iron coil 31 is shown in cross section in order that the manner inwhich the radial field is produced may be illustrated. The longitudinalfield B is produced by field coil 32 and was adjustable in the range of180 to 300 gauss for the region inside coil 31. The ratio of transversefiield intensity B to longitudinal field B v as approximately 0.15maximum along the axis. An electron gun (not shown) was used tointroduce electrons 34 into the end of coil 31. Combinations of beamvoltage (up to l lcv.) and magnetic field B caused the electron beam tobecome a spiral closely approximating the spiral of the coil. The shapeof the electron beam was observed by putting the corkscrew device ofFTGURE 3 in a transparent chamber whose pressure was reduced to 1micron. The ionization produced by the electron beam produced a visibleindication of the path of the beam.

The spiral iron coil 3-1 of FIGURE 3 is shown in cross section toillustrate how the longitudinal field of coil 32 is distorted by spiralcoil 31 to produce a radial field, E

Each cross section can be considered to be a small magnet which has apolarity as shown in FIGURE 3. it is seen that a transverse fieldcomponent B will be produced which to an axially moving particle appearsto rotate in a plane transverse to the longitudinal axis as the particlemoves along the longitudinal axis.

The corkscrew of FIGURE 3 was used in conjunction with a magnetic mirroras shown in FIGURE 4. The coils 41 of the mirror when energized bysources produced magnetic field lines 43 which were of the typeindicated in the figure. A mirror ratio of 1.8, the ratio of the maximumflux density to the flux density at the center of the mirror, wasobtained. The corkscrew 31 was placed in the relatively uniform fieldregion in the center of the mirror and an electron beam 44 produced bysource 55 was injected axially into corkscrew 3?. at an energy up to 1kv. The helical electron beam id produced by a proper combination ofsource energy and field B was reflected by the mirror coils 41. Thisreflection by a mirror of ratio 1.8 indicated that over one-half thebeam energy was in the transverse component of beam 46 beforereflection. Changing either source 45 energy or field B resulted in nospiral and the electron beam passed through mirror coil 41 withoutreflection. Reversing the direction or" magnetic field B produced bycoil 32 so that the handedness of coil 31 was wrong eliminated thespiral 46 and no beam reiiection could be obtained.

It should be noted that the selectivity of the symmetrical structurediscussed above is not good and the single structure can produce bothlarge increases or large decreases in magnetic moment depending on theentrance conditions of the particle. This effect may be intolerable incertain applications.

A rotating transverse magnetic field can also be obtained by winding anelectrically conductive material as a coil of variable pitch. Themagnetic field produced when such a coil is energized has a transversefield which rotates with position along the coil. FIGURE 5 shows such acoil 51 in cross section energized by current from source 52. Themagnetic lines 53 represent part of the magnetic field establishedaround each conductor of coil fill. The heavy direction lines 54:represent the direction of the resultant radial field component with thelength of the lines 54 representing the relative magnitude of thistransverse component of field. It is seen that the radial field becomessmaller as the ratio of pitch to diameter is decreased. For manyapplications, a minimum pitch to diameter ratio of /3 will sufiice.Although there is no 6 theoretical limit on the amount of energy whichmay be transferred to the transverse component of energy, a practicalengineering limit is about of the energy in the transverse component.

The coil of FlGURE 5 has characteristics which may be undesirable incertain applications. Among these characteristics i the increase inlongitudinal field strength in the region of the coil where the pitch issmallest. This effect may be minimized if the coil is being operated ina uniform relatively high field strength region which is produced by anexternal source (which is the usual situation). Another characteristicof the coil of FIGURE 5 is that it is diliicult to obtain a smoothentrance condition for a charged particle entering the coil on the axiof the coil. The radial field existing on the axis tends to divert t 1eparticle from a helix centered about the coil axis, and to introducespurious changes in its magnetic moment.

The variation in longitudinal field strength of the single conductorhelix of FIGURE 5 can be avoided by using a bifilar winding withcurrents in the windings opposite in direction. This cancellation oflongitudinal field also can be achieved by any arrangement of windingswhich has odd and even symmetry with respect to two orthogonal planeswhose line of intersection is along the axis of the coil, where the oddand even refer to direction of current flow. An example of this type ofconstruction is the quadrafilar winding shown in transverse section inFIGURE 6. In addition to the advantages of structural symmetry intermination and lead-in wires, the structure permits the adjustment inthe strength of the transverse field, independent of the change incorkscrew pitch, mere ly by varying the spacing between pairs ofconductors. Thus smooth entrance and exit conditions can be obtainedeasily and the transverse field adjusted for optimum performance.

FlG-URE 6a, b, and 0 show how varying the spacing between the wires A,B, C and D While retaining symmetry about the X and Y planes can producea transverse field 3ll which dillers in intensity but not direction. Thedirection is changed by twisting the Wires along the longitudinal axisof cylinder 32.

A typical design of a quadrafilar type of corkscrew intended to functionwith an electron of 2 lrev. energy with an axial field of genes isinitial pitch-10 cm., diameter-1l cm., length-6i) cm. The design wassuch that if all of the energy was in the transverse component of theelectron, the diameter of the circle thus formed by the electrontrajectory would be about 3 cm. Therefore, the design proceeded on theassumption that the transverse field had no radial dependence. The pitchvaried in a cosine manner from the initial value of 10 cm. to an exitpitch of 2 cm. The current in the coil was approximately amperes.

A corkscrew design useful for winding up an ion of hydrogen of 100 kev.energy may be on the order of 3 feet diameter by 300 feet in length. Thegreater mass and energy of the hydrogen ion as compared to the mass ofelectron is seen to require a much larger physical structure in order tocause the particle to wind up and have a substantial portion of itsenergy in the transverse velocity.

The designs of FIGURES 2, 3 and 6 are merely illustrative of the manypossible coil configurations which can produce transverse fields whichwill cause a charged particle to wind up. It is not necessary for thecoil to be wound on a cylinder of uniform diameter. A cone shaped coilwith the smallest pitch near the largest end of the cone ould be aconfiguration that may be more desirable than that shown in FIGURE 8since the transverse field is strongest in the vinicity of the coilconductors. The equations of motion or" the charged particle are suchthat almost any coil configuration with monotonic decreasing pitch willcause certain particles to wind up. Of course, the length of the coilrequired to cause the particle motion to become synchronous with thecoil pitch to follow while obeying the laws of Newton and Maxwell.

As the corkscrew is made longer, design becomes more critical if perfectresonance is to be maintained. In experimental coil configurations ofturns or less, the pitch variation was not matched properly to theequations of motion to give perfect resonance, yet over half theparticle energy was easily transformed to the transverse compo nent.Computer analysis shows that attempts to scale these same geometricconfigurations to longer systems would be unsuccessful since the energytransfer to the transverse component would decrease as resonance wasmaintained over a smaller fraction of the system length. in effect, thedesign would give a very long zero beat that, in a short system wouldlook like perfect resonance. The longer system wit-h its greaterselectivity, however, would not tolerate the error. Zero beat is definedas that condition where the angle between the vectors representing thetransverse field and the transverse velocity of the particle is notchanging (a condition of resonance).

The quantity (B B (21rL/p), where L is the length of the corkscrewhelix, is related to the fractional change in magnetic moment that canbe produced by the corkscrew. A value of unity for this quantity hasbeen found to be reasonable for designs that have been considered. Theratio of B /B determines the performance characteristics of thecorkscrew. if B /B is large, then L/p is small and the helical coil willhave only a few turns. For this case exact design details are notcritical, a large change in magnetic moment can be produced, but thedevice will accept particles over a broad range of input conditions (notvery selective), and there will be a significant effect on particlesgoing through in the wrong direction (not very unidirectional). If onthe other hand, B /B is small, the system can be highly selective andunidirectional, but since L/p will be large there will be many turns tothe corkscrew. The design is very critical if resonance is to bemaintained over the length of the cork-screw helix. In practical coils,a ratio of B /B in the range of 0.1 to 10% is most likely to be usefulwith a value of 1% considered about right for thermonuclearapplications. Since B has a radial dependency, the change in the ratio B/B as the particle spirals away from the axis must be considered in thedesign.

Corkscrew devices can be constructed which use a twisted electric fieldrather than a twisted magnetic field. An electric field device is shownin cross-section in FIG- URE 7 where the bifilar winding of conductors41 and 42. is energized by voltage source 44 to produce a twistedelectric field 43. A longitudinal magnetic field is also used. There isno essential difference between the electrostatic and magneticcorkscrews except that in the electrostatic case the total particleenergy may change by an amount not exceeding the voltage applied betweenthe conductors. This possible increase of energy and details of theelectric field distribution introduce more considerations into thedesign of the corkscrew.

FIGURE 8 shows a possible application for the corkscrew device where itis desired that a charged particle emerge with a predominantly axialvelocity from the corkscrew. A charged particle source tilt emits a beamof particles 82 which enter a section of a particle accelerator 83wherein a beam of high energy particles 84 is traveling along theaxis 1. The beam 82 has a transverse and axial component of velocityrelative to axis z because of the necessity for placing the source $1ofi axis z. The corkscrew coil 14 and the field from solenoid l2 convertthe transverse velocity component into a longitudinal velocity so thatbeam 32 merges with beam 34 (essentially unaffected by the corkscrew) toform axial beam 85 whose particles are further accelerated. Thus, it isseen that the cork-screw can function as a charged particle unwinder aswell as a winder.

Another application of a corkscrew used as an unwinder is to supply amonoenergetic charged particle beam. Modification of FIGURE 8 may bemade so that there is no beam 84 and section 83 is sealed at the endnear the source 81. A beam 82 from source 81 will contain chargedparticles having a range of energies centered about some center value.In addition there will be some angular dispersion of energy. if thisbeam is sent through the corkscrew structure of FIGURE 8 and unwound andthe corkscrew is selective, the beam 85 emerging from the corkscrew willbe essentially monoenergetic and with very little angular dispersion;The selectivity of the corkscrew is obtained'by making it considerablylonger than necessary and designing its pitch to be a closeapproximation of the pitch of the spiral path of the charged particle.

Although the invention has been described in terms of a device in whicha coil of monotonically changing pitch and uniform axial field intensityhave been used, this is not a necessary limitation. A coil in which thepitch changes in discrete steps will function to cause particle windupalthough not so effectively as a continuously changing pitch coil. Also,there is no absolute requirement that the axial field B be uniform inintensity throughout the length of the variable pitch coil. Of course,since pitch of a charged particle changes with B the coil pitch must bevaried accordingly to match the new particle pitch.

While the invention has been disclosed in specific embodiments and uses,it will be apparent to those skilled in the art that numerous variations.and modifications may be made within the spirit and scope of theinvention and it is not intended to limit the invention except asdefined in the following claims.

What is claimed is:

l. A device for changing the magnetic moment of a charged particlemoving in a static magnetic field with a definable axis comprising meansto supply a field transverse to the axis of said static magnetic fieldat the location of said particle whereby forces act on said particle tochange its path and means to change the direction of said transversefield in accordance with the changing location of said charged particle,along a helical path characterized by decreasing pitch with increasingradius.

2. A device for changing the magnetic moment of a charged particlemoving with a velocity along a helical trajectory in a static magneticfield having a definable axis comprising, a variable pitch helical coilwith spaced turns having its longitudinal axis lying along the axis ofsaid field, means for energizing said helical coil to produce a statichelical field having field components radially transverse to said axisand changing in direction as a function of position along said axis toform a twisted field having a changing pitch along said axis closelymatching the changing pitch of the trajectory of said charged particle,said twisted field radial component being normal to and coincident withthe axially transverse component of velocity of said particle on theparticle trajectory, whereby forces are exerted on said particle tocause said change in its pitch and magnetic moment.

3. A device for causing a charged particle to follow a prescribedtrajectory comprising means for producing a static magnetic field havinga direction and an axis of symmetry, an electrically conductive helixwith spaced turns and a longitudinal axis along said axis of symmetry,said helix producing a field transverse to said longitudinal axis whenenergized by a source of electrical energ said transverse fieldspiralling about said longitudinal axis to correspond to the spiral ofsaid helix, a source of charged particles to inject said particles intosaid helix, said helical field and magnetic field coacting on saidcharged particles to cause the particle to assume a trajectory ofhelical form, the pitch of said trajectory approaching the pitch of saidhelix at least as the particle exits from said helix.

d. A device for changing the magnetic moment of a charged particlemoving on a trajectory in a non-timevarying magnetic field having adefinable axis comprising means for establishing a non-time-varyinghelical magnetic field having field components transverse to said axiswhich change in direction as a function of position along said axis toform a twisted magnetic field with a pitch along said axis closelymatching the changing pitch of the trajectory of said particle moving insaid helical field, whereby the magnetic moment or" said particle isincreased when said trajectory pitch is decreased and decreased whensaid pitch is increased.

5. A unidirectional device for changing the magnetic moment of a chargedparticle comprising, a variable pitch helical coil of electricallyconductive material, the diameter of said coil being not greater thanthree times the minimum pitch of said coil, a current source connectedto said coil to establish a magnetic field having components transverseto the axis of said coil to form a transverse field configuration havingthe same general pitch as that of said helical coil, means for producinga second magnetic field directed along said coil axis, a source ofcharged particles adapted to propel said particles into one end of saidcoil with a trajectory pitch approximating that of said coil end, andmeans controlling said current source whereby said transverse helicalfield and said second magnetic field force said particles to take ahelical trajectory whose pitch is substantially the same as the pitch ofsaid coil.

6. A device for changing the magnetic moment of a char ed particlemoving on a helical trajectory in a static magnetic field with adefinable axis comprising a helical coil of ferromagnetic material ofvariable pitch, said material being smaller in Width than said pitch sothat there is a space between adjacent turns of said coil, said coilhaving a longitudinal axis coincident with the axis of said staticmagnetic field, said coil establishing a secondary magnetic field havinghelical field components transverse to said axis which change indirection as a function of position along said axis to form a twistedfield along said axis closely matching the changing pitch of thetrajectory of said particle moving in said helical field, whereby themagnetic moment of the charged particle is increased for particle motionthrough said coil in the direction of decreasing pitch and decreased forparticle motion in the direction of increasing pitch.

7. The device of claim 6 wherein said secondary magnetic field is thelocalized distortion of the static magnetic field entering and leavingsaid ferromagnetic material.

8. The coil of claim 6 wherein said ferromagnetic material is apermanent magnet with the polarity in the longitudinal direction afterWinding in coil form.

9. A device for changing the magnetic moment of a charged particlemoving along a helical trajectory in a constant magnetic field whosedirection defines an axis, comprising a variable pitch helical coilhaving electrically conducting spaced turns, said coil having itslongitudinal axis lying along the axis of said field,'means for causinga flow of direct current through said coil to establish a helicalmagnetic field having field components transverse to said axis whichchange in direction as a function of position along said axis to form atwisted field with a variable pitch along said axis closely matching thechanging pitch of the trajectory of said charged particle moving in saidhelical field, whereby the magnetic moment of the charged particlechanges from one prescribed value at the entrance to said helical coilto a second prescribed value at the exit.

19. A device for changing the magnetic moment of a charged particlemoving in a static magnetic field comprising means for establishing avariable pitch helical electrostatic field having field componentstransverse to the axis of said helix and changing in direction as afunction of position along said axis to form a twisted electric field,means for producing a magnetic field in the direction of said axis, andmeans for injecting charged particles into said helical electrostaticfield with a trajectory correspondim to the pitch of said helix wherebysaid electric field and said magnetic field force said particle to takea helical trajectory whose pitch follows that of said helical field.

it. A unidirectional device for causing the trajectory of an electronbeam to wind-up comprising a variable pitch helical coil of electricallyconducting spaced turns energized to produce a magnetic field havingcomponents within said coil transverse to the longitudinal axis thereof,said coil being wound in a counter-clockwise direction, an electron gunemitting a beam of electrons with a selected entrance velocity directedalong said longitudinal axis, said electrons entering said coil at theend of greatest pitch, a source of uniform magnetic field directed alongsaid axis and extending throughout said coil, said uniform fieldpolarity being adapted to give said electrons a counter-clockwiserotation, said electrons being diverted from a path along said axis bysaid transverse and longitudinal fields to assume a helical trajectoryof decreasing pitch matching said variable pitch helical field as theelectron progresses with increased magnetic moment along said axis.

12. A device for changing the magnetic moment of a charged particlemoving along a trajectory in a magnetic field comprising, means tosupply a non-time-varying first magnetic field whose lines of force aresubstantially unidirectional, means to supply a second non-timevaryingmagnetic field having an axis of symmetry, said second field having atleast a component normal to said axis, said normal component helicallyspiraling along said axis with changing pitch, whereby said movingcharged particle is caused to assume a spiral trajectory around saidaxis corresponding to said spiraling normal field component.

13. A device for changing the magnetic moment of a charged particlemoving with velocity in a static magnetic field comprising means forproducing said static magnetic field, a helical coil having alongitudinal axis, means for energizing said coil to produce a staticfield component radially transverse to the axis of the coil, said radialfield component changing direction along the axis of the coil to have apitch substantially the same as the pitch of the coil, said radial fieldcomponent causing said particle to change its velocity in a directiontransverse to said coil axis, said transverse particle velocity beingacted upon by the axial field of the coil and said static magnetic fieldto oppositely change its axial velocity to maintain the particle at aconstant velocity, the change in axial and transverse velocities causingsaid particle to assume a helical trajectory corresponding to the helixof said coil.

References Cited by the Examiner UNITED STATES PATENTS 3,005,126 10/61Cutler 3l3---84 JOHN F. BURNS, Primary Examiner.

1. A DEVICE FOR CHANGING THE MAGNETIC MOMENT OF A CHARGED PARTICLEMOVING IN A STATIC MAGNETIC FIELD WITH A DEFINABLE AXIS COMPRISING MEANSTO SUPPLY A FIELD TRANSVERSE TO THE AXIS OF SAID STATIC MAGNETIC FIELDAT THE LOCATION OF SAID PARTICLE WHEREBY FORCES ACT ON SAID PARTICLE TOCHANGE ITS PATH AND MEANS TO CHANGE THE DIRECTION OF SAID TRANSVERSEFIELD IN ACCORDANCE WITH THE CHANGING LOCATION OF SAID CHARGED PARTICLE,ALONG A HELICAL PATH CHARACTERIZED BY DECREASING PITCH WITH INCREASINGRADIUS.